On the northern fringes of the city past the airport, Cheongokdong makes for a pleasant half-day outing combining a ridge hike with a visit to a Buddhist temple. The trail climbs through trees and bracken before breaking onto a ridgeline circling a deep valley. Allow about fifty minutes to reach the summit, where views stretch across Ulsan to the red Hyundai crane in Bangeojin.
After descending, refuel at one of the Korean restaurants in the area, then visit the well-maintained temple nearby. It is not particularly old but offers good photographic opportunities and occasionally has an English-speaking guide. A good option if you are passing through on the way to Gyeongju.
Take bus 102, 422, or 432 to the Cheongokdong terminus and continue on foot.